Pulmonary Aerodynamic Valves: Distribution & Function

This project addresses a major, poorly understood question in vertebrate evolution related to the lung's extraordinary structural diversity, especially the structures that give rise to one-way airflow. Bird lungs have held a special place in this regard, because their design is so radically different from mammalian lungs, and it has been thought that one-way airflow is related to the energetic demands of flight.

However, the lungs of other non-flying vertebrate animals, including snakes, turtles, and chameleons, also differ from those of mammals. This research will provide a better understanding of how aerodynamic valves in the lungs of reptiles give rise to one-way airflow, the physiological significance of these patterns of flow, and their distribution across vertebrate animals.

It will reveal fundamental, form-function relationships linking lung structures to patterns of airflow in reptiles and amphibians; enhance understanding of the effects of these patterns of airflow on gas exchange, respiratory water loss, and heat loss; and be applied to reconstruction of the respiratory systems of extinct tetrapods. The project also includes significant educational and outreach activities, including science communication training for lab personnel, participation in public-education, distance-learning programs run by Utah's Hogle Zoo, and development of virtual reality infrastructure for research, outreach, and teaching.

Three primary activities will result from the proposed research. (1) A phyletic survey will be made of patterns of airflow in the lungs of amphibians and reptiles. (2) Tests of the following hypotheses for the mechanistic basis of pulmonary aerodynamic valves will be made by measurements and visualizations of patterns of airflow, computational fluid dynamics simulations, and physical models: i) that turtles have a pulmonary Tesla valve; ii) that the expiratory valve of archosaurs functions like an internal nozzle, where a Coanda surface induces and amplifies flow; iii) that the expiratory valve arises from a caudal guiding dam. (3) Balloon catheters will be implanted into the lungs of alligators which will allow unidirectional flow to be converted to tidal airflow. Under these two flow regimes hypotheses for the functional significance of aerodynamic valves will be tested: i) that alligators have counter-current or cross-current gas exchange; ii) that unidirectional flow reduces rates of evaporative water and heat loss, and improves wash-out of lung CO2 and wash-in of O2.

Measurements will made of O2 extraction and CO2 removal with each breath, rates of lung washout of CO2, rates of respiratory evaporative water loss and heat loss, and rates of ventilation relative to rates O2 consumption and CO2 excretion. The proposed research has four strands of educational and outreach broader impacts: 1) Recruitment of underrepresented participants into STEM; 2) Training of lab personnel in science communication, working closely with the Natural History Museum of Utah; 3) Outreach to the lay community, including K-12 schools, through distance-learning programs of Utah's Hogle Zoo; 4) Development of virtual reality infrastructure for research, outreach, and teaching.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.